1. Field of the Invention
This invention relates to practice golf clubs and, more particularly to practice golf clubs having a hinge manufactured in the shaft.
2. Description of the Related Art
One or two-way hinge golf clubs have been developed in the past to improve a golfer's golf swing. With such clubs, a hinge is manufactured in the shaft which allows the lower section of the shaft to pivot relative to the upper section when the golf club is improperly swung. Centrifugal forces exerted on the upper and lower sections of the shaft during an improperly executed swing causes the sections to pivot at the hinge. By monitoring if and when the upper and lower sections pivot during the swing, one can determine whether the swing is properly executed.
One or two-way hinge golf clubs have been developed as disclosed in U.S. Pat. Nos. 2,497,237, 3,033,575, 4,854,585 and 4,856,782. One problem with two-way hinge golf clubs which allow the upper and lower sections of the shaft to pivot in the forward or rearward direction, is that they are difficult to use as instructional aids.
One problem with all types of hinge golf club developed heretofore is that manufacturing, tolerances of the individual hinge members must be very relatively small so that hinge operates correctly. Such small tolerance requirements, of course, lead to increased manufacturing costs. For example with many hinged golf clubs, the hinge members must be properly manufactured so that the upper and lower sections of the shaft always return to a longitudinally aligned position during use. Also, the hinge members must fit together tightly so that the hinge does not wobble or pivot to freely during use. If the hinge pivots too "freely", small external forces, such as gravity and wind, exerted on the upper and lower sections of the shaft or the clubhead, cause the sections to pivot thereby giving the user inaccurate information regarding his or her swing. Still another problem with such golf clubs is that with continuous use, adjacent surfaces in the adjoining hinge members become worn which causes additional "play" in the hinge.
Ideally, the hinged golf club should be lightweight with the hinge itself being made of the same material as the shaft of the golf club, namely stainless steel. One problem however with hinges made of stainless steel material, is that the rubbing surfaces become "galled" over a short period which may effect the pivoting action.
In summary, a one way hinge golf club is needed in which the hinge is made of stainless steel material that uses hinged members which can be manufactured with greater tolerance. Also, the hinged golf club must be sufficiently durable to withstand normal wear and tear forces so that excessive "play" does not develop with continuous use. Also the hinge must be designed so that the lower and upper sections of the shaft always return to a longitudinally aligned position. It is also desirable that the hinge have means to prevent undesirable pivoting when using either an opened or closed club head.